Hypoplastic Left Heart Syndrome (HLHS) is a severe and devastating heart defect that affects ~ 1 in 10,000 children born each year. The mechanism(s) leading to pathogenesis of HLHS and associated left-sided cardiac pathology remain unknown. The goal of this proposal is to test a novel hypothesis that states HLHS is an expression of rheumatic heart disease (RHD) in the fetus. In RHD, among other immunologic processes, anti-streptococcal antibodies are generated in response to strep infection. In genetically susceptible hosts these antibodies then cross-react with left-sided myocardial and valvular antigens through a mechanism known as molecular mimicry. We propose similar mechanism for the pathogenesis of HLHS in which maternal antibodies produced in response to antecedent (and recurrent) strep infection, cross the placenta and damage the fetal heart in the susceptible host. Our preliminary data suggest not only a strong association between HLHS and prior maternal strep infection, but also elevated anti-human cardiac myosin serum titers in mothers of HLHS babies (as found in patients with rheumatic fever), compared with three control groups. To extend these studies, we will compare groups of pregnant women referred for fetal echocardiography (echo) and found to have a pregnancy affected by (1) HLHS; (2) congenital heart disease other than HLHS; and (3) nothing (i.e., normal fetal echo, referred controls). A fourth group (random controls) are recruited from the general population early in pregnancy (<18 weeks) to overcome the obvious selection biases in the referred controls. In Aim 1 we determine if mothers of babies with HLHS have a significant history of strep infections through a questionnaire tool, review of maternal medical records and measurements of blood titers of an anti-streptococcal antibody (ASO). In Aim 2, using serum from the repository of samples obtained from the 4 groups of subjects in Aim 1, we will also compare antibody reactivity with a variety of valvular/myocardial antigens (shown to be involved in RHD lesions); these are then compared to matched serum samples obtained from the babies after birth. In Aim 3, we determine if heart reactive antibodies and inflammatory markers (TNF-alpha, INF-gamma and IL-4) implicated in valvular lesions in RHD are also present in myocardial tissue specimens obtained from HLHS babies (at the time of neonatal surgical intervention). Immunohistochemical analysis of neonatal heart tissues will be performed to assess for the presence of immunoglobulin deposition and other immune markers. The candidate: Dr. Eghtesady is a pediatric cardiothoracic surgeon who has had long standing interest in the pathogenesis of HLHS and its medical/surgical management. Pertaining to the proposed studies, his long-term career goal is to improve the quality of life for the children and families affected by this severe and devastating ongenital heart disease. The research environment: CCHMC and The Heart Institute (THI) of CCHMC are dedicated to improve child health and transform delivery of care through fully integrated, globally recognized research, education and innovation. The mission of CCHMC is to achieve the best medical and quality of life outcomes, patient and family experiences and value, for patients from the community, the nation and the world. For this reason, the success of studies such as proposed is of high priority to CCHMC and the HI. Significant resources are provided for this purpose with great commitment to ensure a thriving environment that allows for extensive collaborative arrangements, as in this study. Dr Eghtesady's clinical schedule has been structured to afford him 50% protected time for research. In 2007, CCHMC was awarded full accreditation by the Association for the Accreditation of Human Research Protection Programs confirming the strength and commitment to clinical research programs. Finally, in 2008, the HI Clinical Research Core was established to specifically see through the success of ongoing clinical studies, through rigorous oversight and provision of additional resources. Relevance: Each year, 1 out of 100 children born is affected by a congenital heart disease. Among these, HLHS is perhaps the most severe and devastating, significantly impacting the lives of affected families. Tremendous resources are devoted to its medical management. Therefore, understanding why HLHS happens, the goal of the proposed research would have great significance and relevance to public health.